1. Field of the Invention
This invention relates generally to so called "cantilevered" rolling mills, where the work rolls are mounted in an overhung fashion on the ends of roll shafts which protrude from housings containing the shaft bearings, gears, roll parting adjustment mechanisms, etc. The invention is concerned in particular with an improved dual lip shaft seal assembly for preventing leakage of lubricants from such housings and for preventing ingress of external contaminants, e.g., cooling water and entrained dirt, mill scale, etc.
2. Description of the Prior Art
FIGS. 1 and 2 are illustrative of a typical prior art mill and shaft seal arrangement.
Roll shafts 10 are journalled between sleeve bearings 12 supported in rotatable eccentrics 14a, 14b. The eccentrics in turn are journalled respectively for rotation in the front and rear plates 16a, 16b of a housing 18. The roll shafts 10 carry gears 20 which mesh with other gears (not shown) forming part of the mill drive.
The roll shafts have ends protruding externally through the front housing plate 16a. These protruding ends include truncated conical portions 10, on which grooved work rolls 22 are removably secured by means of tapered sleeves 24 axially wedged therebetween. Transversely extending keys 26 bear against the outboard flanks of the rolls and are held in place by set screws 28 threaded into the ends of the roll shafts. Covers 30 enclose the keys 26 and the outboard ends of the sleeves 24. The covers are held in place by caps 32 threaded onto the shaft ends. Simultaneous rotation of each roll shaft's eccentrics 14a, 14b in opposite directions serves to symmetrically adjust the roll shafts and the work rolls carried thereon with respect to the mill pass line.
During operation of the mill, lubricant is applied to the shaft bearings and the eccentrics from within the housing, and cooling water is applied to the work rolls exteriorly of the roll housing. Dual lip seal shaft assemblies 34 serve to retain the lubricant within the housing while at the same time excluding cooling water and entrained mill scale, dirt, etc. from penetrating into the housing interior. As can be best seen in FIG. 2, each seal assembly 34 includes a pair of metal flingers 36, 38 surrounding the roll shaft and interposed between the inboard flank of the work roll 22 and the respective adjacent shaft bearing 12 and eccentric 14a. The flingers have generally L-shaped cross-sectional configurations, with abutting base portions 36a, 38a and with radially extending axially spaced flanges 36b, 38b defining confronting annular contact surfaces 36c, 38c. The flinger base portions are supported on a cylindrical land L.sub.a machined into the shaft surface at a location between the larger diameter portion journalled for rotation in the adjacent bearing 12 and the truncated conical portion 10' on which the work roll 22 is removably mounted by the tapered sleeve 24 interposed therebetween. Land L.sub.a has an axial length l.sub.a. A seal end plate 40 is fastened to the housing end plate 16a. The seal end plate has a pair of openings 42 through which the roll shafts protrude.
The openings 42 are concentric with the rotational axes of the eccentric bearing sleeves 14a. Seal holders 44 are journalled for rotation in the openings 42, and are mechanically tied to the eccentric sleeves 14a for rotation therewith by means of machine screws 46 or the like. The seal holders have inwardly extending radial flanges 44' surrounding the roll shafts. The inner rims of the flanges 44' are grooved as at 44" to receive circular radially outwardly protruding beads on the base portions of seals 48 having dual oppositely facing axially separated lips 48a, 48b. The inner edges of the flanges 44' and the seals 48 mounted thereon are arranged coaxially with the rotational axes of the roll shafts.
The flingers 36, 38 rotate with the roll shafts, and the seals 48 remain fixed in relation to their respective seal holders 44, the latter being tied to the eccentric sleeves 14a which only are rotated to achieve adjustment of the roll parting. Contact between the outboard seal lip 48a and contact surface 36c serves to exclude cooling water and entrained particulates from the housing interior, whereas contact between the inboard seal lip 48b and contact surface 38c serves to retain lubricants within the housing.
The major drawback with this arrangement stems from the need to extend the length l.sub.a of the land L.sub.a in order to accommodate the axially spaced seal lips 48a, 48b acting on the confronting contact surfaces 36c, 38c of the two flingers 36,38. More particularly, and with reference to FIG. 9, it is commonly accepted that in cases of the type herein under consideration, where shafts are subjected to combined reverse bending and steady torsion, the bending moment "M" at plane "X--X" is equal to SF l, where "SF" is the separating force resulting from rolling and "l" is the sum of "l.sub.a " and "l.sub.c ". For a given bending moment design limit, SF is inversely proportional to l. Since l.sub.c is a minimum dimension dictated primarily by the strength of the roll material, in order to increase the rolling capacity of the mill, it becomes essential to shorten l.sub.a as much as possible.